Imaging devices, including charge coupled devices (CCD) and complementary metal oxide semiconductor (CMOS) sensors, among others, have commonly been used in photo-imaging applications. Non-limiting examples of CMOS imaging circuits, processing steps for fabrication thereof, and the functions of their components are described, for example, in U.S. Pat. No. 6,140,630 to Rhodes, U.S. Pat. No. 6,376,868 to Rhodes, U.S. Pat. No. 6,310,366 to Rhodes et al., U.S. Pat. No. 6,326,652 to Rhodes, U.S. Pat. No. 6,204,524 to Rhodes, U.S. Pat. No. 6,333,205 to Rhodes, and U.S. Pub. No. 2006/0198008.
FIG. 1 is a circuit diagram illustrating a non-limiting example of a conventional four-transistor pixel cell 120 which may be used in a CMOS imaging device. During an integration period, light strikes the photosensor 124 to generate charges stored within an accumulation region of the photosensors. After the integration period and in response to a charge transfer signal TX, a charge transfer transistor 128 gates the photogenerated charges from the accumulation region to a storage node 126 which may be configured as a floating diffusion region. The transferred charges bias the gate, of a source follower transistor 132, which has a first terminal connected to a voltage source 130 (e.g., VDD) and a second terminal that transmits an output signal Vout indicating the amount of charge stored in the floating diffusion region 126. In response to a row select signal ROW, a row select transistor 134 gates the output signal Vout to a column line 136. In operation, the storage node 126 is reset by a turning on a reset transistor 142 connecting the voltage source 130 and the storage node 126, and a reset signal Vrst is consequently output as the output signal Vout. When the photosensor charge is transferred to the storage node 126 an image signal Vsig is output as the output signal Vout.
FIG. 2 is a block diagram illustrating a non-limiting example of a conventional CMOS imager system 40. As shown, the imager system 40 includes a pixel array 30 is connected to a row decoder/selector 42 and column bus 43 and a timing and control circuit 44 for controlling the row decoder/selector 42 and column bus 43. The output signals Vout (Vrst, Vsig) of the pixel cells are read out row-by-row. During readout, each pixel cell of a selected row transmits an output signal Vout, via its respective column line 136, to the column bus 43. The output signals Vout include the reset signal Vrst and the image signal Vsig, each of which are sent to a sample and hold circuit 45 controlled by the timing and control circuit 44. After the sample and hold circuit 45 acquires the reset Vrst and image Vsig signals for a pixel cell, those signals Vrst, Vsig are converted to a differential signal (Vrst-Vsig) by a differential amplifier 46, the differential signal (Vrst-Vsig) is digitized by a digitizer 47, and the digital pixel data is provided to an image processor 48.
FIG. 3 is a cross-section view illustrating a non-limiting example of a portion of a conventional microlens system 200, which may be used for a pixel array of an imaging device, including, but not limited to, that shown in FIG. 2. The FIG. 3 cross section is taken across a row of alternates red and green pixels in pixel array 30. As shown, respective convex microlenses 112 and color filters R, G of a Bayer color filter array are provided to each of two illustrated pixel cells 120 separated by isolation trenches 154. The Bayer color filter pattern provides a red, green, or blue filter to the pixel cells of a pixel array, such that only light of a respective wavelength range passes through a filter for detection. During image capture, a camera lens 111 transmits light of an image to the underlying convex microlenses 112, which in turn direct the light onto respective photosensors 124 of the pixel cells 120. In FIG. 3, for example, an incident light beam Lla is transmitted from point A of the camera lens 111 to the microlens 112 of the green pixel, and the light is then redirected as light beam L1b through the green filter G and onto to the right-side photosensor 124. When light contacts the photosensor 124 having a p-type region 124a and underlying n-type region 124b forming a photodiode, photogenerated electrons accumulate in the n-type region 124b. 
Light may enter a desired pixel cell 120 but still fail to reach a respective photosensor 124. This may result, for example, from imperfections in the camera lens 111 and microlenses 112, from the arrangement of the camera lens 111 and microlenses 112, or from internal refractions within upper fabrication layers of an integrated circuit containing the pixel array 30. In FIG. 3, the camera lens 111 transmits a light beam L2a (again from point A) at an angle askew to the lens axis 113 of the receiving microlens 112. Consequently, the light beam L1a is redirected as a “leaking” light beam L2a (i.e., a light beam which is not aimed by a microlens 112 at a photosensor 124) and will not be detected. A microlens system for redirecting leaking light is desired.